Retinal axons which form a topographic projection from the eye to the optic tectum can be induced, by a restricted retinal lesion, to shift their termination sites toward the resulting deafferented region in the tectum. The experiments in this proposal will use time lapse imaging to observe the deafferentation-induced morphological changes of individual axons in living Xenopus tadpoles in order to analyze how changes in branch elaboration and elimination contribute to reorganizing the retinotectal projection. The respective contributions to map reorganization of neural electrical activity and of calcium- calmodulin kinase II activity, a potential downstream signal for correlated neuronal activity, will be tested by observing the consequences on axonal reorganization of blocking them. To determine whether axons that come to innervate the previously deafferented tectal region recapitulate the developmental program of initially forming NMDA-only silent synapses , the proportion of silent synapses will be measured in the part of the tectum reinnervated by shifting connections and compared with controls. These experiments will provide new insights about the mechanisms by which tectal innervation is regulated during development.